Climate models keep getting better but still can't predict with great certainty. So scientists run multiple models and look at the results of each model and calculate a consensus projection. The intent is to reduce the level of uncertainty by using a range of models with different types of shortcomings to hopefully improve confidence in the results.

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The seesaw variability of global temperatures often engenders debate over how seriously we should take climate change. But within 35 years, even the lowest monthly dips in temperatures will be hotter than we've experienced in the past 150 years, according to a new and massive analysis of all climate models. The tropics will be the first to exceed the limits of historical extremes and experience an unabated heat wave that threatens biodiversity and heavily populated countries with the fewest resources to adapt.

Ecological and societal disruptions by modern climate change are critically determined by the time frame over which climates shift. Camilo Mora and colleagues in the College of Social Sciences'Department of Geography at the University of Hawaii at Mānoa have developed one such time frame. The study, titled "The projected timing of climate departure from recent variability," will be published in the October 10, 2013 issue of Nature and provides an index of the year when the mean climate of any given location on Earth will shift continuously outside the most extreme records experienced in the past 150 years.

The new index shows a surprising result. Areas in the tropics are projected to experience unprecedented climates first — within the next decade. Under a business-as-usual scenario, the index shows the average location on Earth will experience a radically different climate by 2047. Under an alternate scenario with greenhouse gas emissions stabilization, the global mean climate departure will be 2069.

"The results shocked us. Regardless of the scenario, changes will be coming soon," said lead author Camilo Mora. "Within my generation, whatever climate we were used to will be a thing of the past."

The scientists calculated the index for additional variables including evaporation, precipitation, and ocean surface temperature and pH. When looking at sea surface pH, the index indicates that we surpassed the limits of historical extremes in 2008. This is consistent with other recent studies, and is explained by the fact that ocean pH has a narrow range of historical variability and because the ocean has absorbed a considerable fraction of human-caused CO2 emissions.

The study found that the overarching global effect of climate change on biodiversity will occur not only as a result of the largest absolute changes at the poles, but also, perhaps more urgently, from small but rapid changes in the tropics.